Field of the Invention
The present invention is directed to a modularly-constructed integrated services digital network (ISDN) communication system of the type having at least one switching unit comprising a switching network and to which apparatus networks can be connected via peripheral modules. The communication system has a memory-programmed system processor and comprises a real-time operating system for controlling program subsystem for controlling program subsystems provided for the execution of communication technology-associated functions and for the control of an idle task program subsystem that is fashioned as a branch subsystem for a transition to a subscriber operating system. It also has a system memory that comprises memory segments addressable via descriptors which has a system table memory that contains system table descriptors referring to memory segments of the real-time operating system and has a further system table memory that contains real-time interrupt descriptors for events pertaining to the real-time operating system and a module table memory that can be selected alternatively to the system table memory and that contains module table descriptors referring to memory segments of the subscriber operating system. The module table memory also contains communication descriptors referring to intercommunication segments of the real-time operating system; these communication descriptors can be interpreted identically with the system table descriptors contained in the system table memory and referring to the intercommunication segments and among which at least one code segment descriptor for access onto the code segment of the first branch subsystem, one status segment descriptor for access onto the status segment assigned in the real-time operating system to the branch subsystem, and one data segment descriptor for access onto an intercommunication data segment are located, this intermediately storing the input information required by each of the two operating systems given a transition to the respective other operating system.
The system has a further module table memory that can selected alternatively to the other system table memory and that contains TS interrupt descriptors for events pertaining to the subscriber operating system, and having control statements in the first branch subsystem that, given activation of the branch subsystem, trigger an assignment change of the system processor from the system table memory to the module table memory and, upon call-in of a status segment descriptor, subsequently effects a process change into the interrupt transition routine that is subsequently ended, control statements in the interrupt transition routine that, given activation of the interrupt transition routine and upon call-in of the communication status segment descriptor, initiates a process change into the first branch subsystem, further control statements in the branch subsystem that effect an allocation change of the system processor from the module table memories to the system table memories. The invention is particularly characterized in that a program subsystem having comparatively high priority is fashioned in the real-time operating system as a further or second branch subsystem, in that the second branch subsystem, given the respective arrival of a first periodic event, assumes a ready state in order to be assigned to the system processor in the real-time operating system for execution, that the further module table memory contains at least one interrupt descriptor for a second periodic event following the first periodic event, said at least one interrupt descriptor referring to the interrupt transition routine, that the further module table memory contains interrupt descriptors for events pertaining to the real-time operating system, said interrupt descriptors referring to an interrupt rescue routine in the subscriber operating system, and in that, following the assignment change of the system processor from the module table memories to the system table memories, the second branch subsystem assumes a dormant condition provided in the real-time operating system as a non-ready task condition.
The European patent application 0 333 123 basically discloses such a communication system that controls the communication system-associated operations and tasks with the assistance of a real-time operating system and additionally comprises a subscriber operating system that is coupled to the real-time operating system such that, first of all, the data and data applications administered by the real-time operating system can be prioritized over the access of the subscriber operating system and, secondly, the data applications conducted under the subscriber operating system can be inserted into the communication system without additional adaptation expense. Due to the implementation of a subscriber operating system, for example of the operating system XENIX, the communication system has therefore been lent a double function; it continues to handle the communication-oriented jobs and is additionally available for individual program development and data processing in the sense of a general data processing (DP) system.
A common processor device is provided in the known communication system for both operating systems, communication-oriented jobs to be handled in this common processor device under the administration of the real-time operating system and this common processor device being made available to the subscriber operating system in those times in which no functions related to communication technology are to be satisfied.
In order to enable a continuous transition between the two operating systems, certain descriptors constructed in accordance with the addressing mechanism of the system processor are identically fashioned for both operating systems. The actual program-oriented transition from the real-time operating system into the subscriber operating system occurs in a modified program subsystem of the real-time operating system. In order to assure that time-critical or real-time functions of the real-time operating system are handled with priority over all functions of the subscriber operating system, the idle task program subsystem of the real-time operating system in the known communication system is fashioned, so to speak, as a branch for a transition into the subscriber operating system. What this means is that a transition can occur only when the real-time operating system has activated its idle task program subsystem, i.e. when no jobs are pending.
The transition from the subscriber operating system back into the real-time operating system is then initiated by an event (interrupt) that is directed to the real-time operating system. In order to be able to transfer data from one operating system into the other, an intercommunication data segment is provided that exercises a "mailbox function". For example, events directed to the subscriber operating system must be intermediately stored in the intercommunication data segment while the real-time operating system is being worked off in order to then be capable of being processed by the subscriber operating system after a transfer thereinto.
In the known communication system, the processing capacity of the system processor being assigned to the subscriber operating system is essentially dependent upon how high the load on the communication system is as a result of communications technology-associated jobs. Therefore, no calculations can be made, nor can any particulars be provided regarding the time interval which processing of a respective program in the subscriber operating system will occupy.